Unburned fuel and other combustion products may escape past the piston of an internal combustion engine (e.g., an internal combustion engine of a vehicle) into the crankcase. The resulting gases in the crankcase, often referred to as “blowby” gases, may contribute to the formation of sludge in the engine oil supply. Further, blowby gases may excessively pressurize the crankcase, resulting in undesirable leakage of oil pan gasket and crankcase seals.
To avoid these issues, an engine may include a positive crankcase ventilation (PCV) system coupled to the intake, which serves to vent blowby gases from the crankcase to the intake. The PCV system may include a PCV valve arranged intermediate the crankcase and the engine intake passage, to regulate the flow of blowby gases from the crankcase to the intake manifold. Various types of PCV valves may be used in PCV systems to regulate crankcase ventilation flow. One standard PCV valve configuration includes three different-sized orifices. A large orifice is arranged in series with a variable pressure control valve. The series arrangement of the large orifice and the variable pressure control valve is arranged in parallel with a small orifice. This parallel arrangement is arranged in series with a parallel arrangement of a tiny orifice and a check valve, the check valve configured to allow flow from the crankcase to the intake manifold to the engine intake passage and restrict flow from the engine intake passage to the crankcase. In the case of low intake manifold vacuum, the variable pressure control valve opens and allows air flow through the large orifice. In this condition, the engine can accept the larger air flow rate, which is near the target crankcase ventilation flow rate. In the case of negative intake manifold vacuum (positive pressure), air flow passes from the intake manifold to the crankcase through the tiny orifice. In the case of high intake manifold vacuum, the variable pressure control valve shuts, and gasses flow from the crankcase to the intake manifold through the small orifice. Thus, the PCV valve limits the flow of crankcase ventilation air into the intake manifold during idle conditions, to reduce the idle air flow rate and thereby limit engine air consumption at idle. The limited flow of crankcase ventilation air into the intake manifold during idle conditions may ensure that adequate engine air flow budget is left over for other flows entering the engine intake downstream of the throttle such as fuel vapor purge flow and flow from an aspirator which serves to generate brake booster vacuum, such that coordination/arbitration of the various throttle bypass flows is not needed.
However, the inventors herein have recognized potential issues with such systems. For example, while the limited crankcase ventilation flow occurring via the small orifice during idle conditions may be appropriate during minimum engine air flow conditions (e.g., during warm idle conditions with the transmission in neutral and low front end accessory drive (FEAD) loads), these conditions may be relatively rare. Indeed, in some start/stop engines, these conditions may be almost extinct. The design of the standard PCV valve described above, which limits crankcase ventilation flow during all idle conditions to a level appropriate for minimum engine air flow conditions, may be undesirable for several reasons. For example, the amount of crankcase ventilation flow which is appropriate for minimum engine air flow conditions may not provide adequate crankcase ventilation during other idle conditions, e.g. when intake manifold vacuum is in the range of 20-80 kPa. Further, in the context of gasoline direct injection engines, increased crankcase ventilation may be desirable due to fuel dilution which may occur during warm-up or in cold weather conditions. For example, during such conditions, crankcase oil may be diluted by un-combusted injected fuel which enters the crankcase. Furthermore, the efficiency of oil separators may be highest in a narrow flow rate band, and thus a constant and adequate crankcase ventilation flow rate may increase oil separation. The oil separation is typically poor when flowing through the small orifice, since this results in low velocity through the oil separator.
In one example, the issues described above may be addressed by a method for an engine including electrically controlling a crankcase ventilation valve to selectively enable crankcase ventilation flow into an engine intake downstream of a throttle based on desired engine air and fuel flow rates, current engine air flow rate contributions from a brake booster, and current engine air and fuel flow rate contributions from a fuel vapor purge system. In this way, rather than restricting crankcase ventilation flow to a level that is acceptable during minimum engine air flow conditions, crankcase ventilation flow may be actively controlled via electrical control of the crankcase ventilation valve such that higher levels of crankcase ventilation flow are achieved during conditions where such flow will not result in engine air flow rate and/or fuel flow rate exceeding a desired amount for current engine operating conditions. Put another way, engine operating conditions in which crankcase ventilation flow will result in excessive engine air flow/fuel flow may only occur when the transmission is neutral, the engine and catalyst are warmed up, and FEAD load is below a threshold. Accordingly, active control of a crankcase ventilation valve may result in increased crankcase ventilation flow, which may advantageously increase crankcase ventilation and oil separation and reduce fuel dilution. The electrical control of the crankcase ventilation valve may be achieved via control of a solenoid valve integrated in the crankcase ventilation valve. The crankcase ventilation valve may further include one or more orifices integrated therein, and may further include a variable pressure control valve in some examples.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.